Problem: It takes 15 men working steadily 4 days to dig the foundation for a new apartment.  How many days would it have taken 25 men working at the same rate to dig the foundation?  Express your answer as a decimal to the nearest tenth.
Answer: The number of men and the amount of time to dig the foundation are inversely proportional.  Let $m$ equal the number of men and $d$ equal the number of days to complete the foundation.  This implies that $md=k$ for some constant $k$.  From the given information, $15\cdot 4=60=k$.  Knowing the value of $k$ we can solve for the number of days it would have have taken 25 men to dig the foundation: \begin{align*}
25\cdot d&=60\\
\Rightarrow\qquad d&=60/25=12/5=\boxed{2.4}
\end{align*}